An electrocardiogram (ECG) of a single heartbeat is commonly referred to as a PQRST complex. The PQRST wave includes a P-wave that corresponds to activity in the atria, a QRS complex that represents the electrical activation of the ventricles, and a T-wave that represents the electrical recovery or recharge phase of the ventricles. The QT interval is the time between the QRS onset and the end of the T-wave, and is commonly measured for purposes of evaluating cardiac electrical stability and thereby predicting potentially life threatening medical conditions such as cardiac arrhythmia. Some pharmaceuticals have side affects that increase the QT interval of an otherwise healthy patient and induce unstable cardiac electrical activity. Therefore, the FDA has begun to perform a drug-induced QT study on new pharmaceuticals prior to their approval. One problem is that an increase in QT interval is not directly correlated with cardiac electrical instability and another problem is that the QT interval is difficult to precisely measure. Therefore, if we only rely on the QT interval, there is the potential for the exclusion of beneficial pharmaceuticals based on the erroneous assumption that they may cause electrical instability and malignant cardiac arrhythmias.
Studies have shown that an increase of heterogeneity in the re-polarization of the heart is directly linked to cardiac electrical instability. Accordingly, an attempt has been made to find the ECG features which have a higher correlation with the heterogeneity of the re-polarization as an indicator of cardiac electrical instability. More recently, it has been determined that the shape of the T-wave is an ECG feature that can be evaluated to more accurately asses cardiac electrical stability. As an example, T-wave flatness, asymmetry, and the presence of a “notch” in the T-wave have been correlated with unstable cardiac electrical activity. The problem is that, although T-wave shape observation has the potential to more accurately assess cardiac electrical stability, its consistency relies on the quality of data defining the T-wave. For example, a twelve lead ECG provides 12 separate T-waves representing different electrical views/projections of cardiac re-polarization. Therefore, if the optimal and most consistent T-wave representation is not implemented for observation, it will be difficult to assess a re-polarization abnormality based on any particular lead.
Another problem relates to the placement of the sensors or transducers on a patient for the purpose of monitoring the electrical activity of the patient's heart. The conventional process involves placing multiple sensors at a variety of locations selected to optimally monitor the electrical activity. As the optimal sensor placement location varies during the course of the electrical cycle, and varies from patient to patient, it is currently not feasible to ensure that a sensor is placed at every optimal location for every patient.